Aluminum-zinc-magnesium alloy



United States Patent Ofi ice 3,414,407 Patented Dec. 3, 1968 3,414,407 ALUMllNUM-ZIN'C-MAGNESTUM ALLOY Albert Jager, Rome, N.Y., assignor to Revere Copper and Brass Incorporated, New York, N.Y., a corporation of Maryland No Drawing. Filed Apr. 26, 1966, Ser. No. 552,363 3 Claims. (Cl. 75-146) This invention relates to aluminum-base alloys and, more particularly, to an aluminum-zinc-magnesium alloy Of improved extrudability and utility.

Extrudable free machining alloys, which are particularly useful as machine screw stock, are presently available in three diflerent aluminum-base systems, to wit,

die container temperature was 800 F. The extrusion was quenched by an air blast at the die, and the extrusion ram speed was held at 33 feet/ minute.

By comparing the breaking pressure for Alloy 1 with aluminum-copper, aluminum-copper-magnesium and alu- Alloy 2, and for Alloy 3 with Alloy 4, it will be seen minurn-magnesium-silicon. The machinability of each of that the addition of lead and bismuth improved extrudathese alloys is further improved by the addition of a bility of the base alloy at any specified billet temperature. small amount of lead or bismuth, or both. However, it The improved utility of the alloys Of the Present is a characteristic of each of these alloy systems that ven ion is Shown by the data in Tables II, III and IV air quenching at emergence from the extrusion dies does wherein Certain Properties of y agnot develop optimum tensile strength, and accordingly nesium alloy are compared with those of the aforemenrod extruded from these alloys, when it is to be used as tiohed Prior art alloys based on the min pp r and machine screw stock, must be solution heat treated to aluminum-magnesium-silicon systems. The aluminumdevelop its tensile strength. Zinc-magnesium alloy representative of the invention con- An aluminum-base alloy system consisting essentially a d Zinc, magnesium, 05% lead, 05% of aluminum, zinc and magnesium has been developed bismuth, and the balance aluminum except for less than heretofore but has not exhibited suitable extrudability 1% impurities consisting primarily of iron and silicon. and machinability to justify its use as machine screw stock the pri r art aluminum-copper alloy contained 5.5% copor the like. However, I have now discovered that when per, 05% l nd 0. bismuth, balance essentially the zinc and magnesium contents of this system are mainaluminum, and the Pfior art flhlminum'magnesiu'm-silitained within relatively close limits, to wit, about 2% to C n alloy contained 1.0% magnesium, 0.64% silicon, 5.5% zinc and about 0.25% to 2.5% magnesium, the 0.5% bismuth, 0.25% copper, 0.10% chromium, balance extrudability and utility of this aluminum base alloy aluminum. Each of these alloys was hot extruded at system is unexpectedly improved by the addition of about about 850 F. When indicated to be quenched at the ex- 0.3% to 2.5% of lead or bismuth, or both. trusion die, they were quenched by a blast of compressed Lead and bismuth are known aids for improving the air at ambient temperature; when indicated to be solution machinability of various alloy systems, and they perform heat treated, they were furnace heated to about 950 F. similarly in the system 25.5% zinc, 0.252.5% magand then water quenched. Following the specified treatnesium, balance essentially aluminum. However, both ment, each extruded alloy was naturally aged at ambient lead and bismuth, alone or in admixture and in total 40 mperature for4days.

' TABLE II Property Condition AlxlfiltgyZn fiilglyu Alxlggysi (Ks-i) --{$313535ittibtfiiftfibiii?agar;j: 2%.? ii? 521% Quenched at die, naturally aged 27. 9 23.9 21, g "{Solution heat treated, naturally a ed-.. 32.1 32.7 27.6 W --{atriaanaest esiaa.---- an at at ---{353F313iittfiatiif fiiibihfirged. I 333 22" 2312 amount of between 0.3% and 2.5%, also improve the extrudability of the base alloy as can be seen from Table I. In this table, extrudability is indicated by the breaking pressure required to initiate extrusion at a specified billet temperature, lower breaking pressure representing better extrudability. Each of the alloys contained less than 1% impurities consisting primarily of iron and silicon. In each instance bookmold billets of the alloys 3% inches in diameter were homogenized by holding them at 815-865 F. for about 12 hours. After cutting each billet to an 11 inch length, one billet of each composition was extruded at each of two temperature levels (825 F. and 875 F.) to 7 inch rod. The preheat time for each extrusion was 2 hours at temperature and the From the data of Table II it is apparent that the alloy of the invention attained substantially its ultimate tensile strength (U.T.S.), yield strength (Y.S.), elongation and reduction of area (R. of A.) merely by air quenching at the extrusion die, whereas both of the prior art alloy systems required solution heat treatment to develop these properties to comparable levels. A solution heat treatment is not required by the alloys of the invention because of their lower critical cooling rate compared to those of the prior art alloys.

The alloys referred to in Table II were similarly compared under the same conditions except for the addition of a 21% cold drawing operation after extrusion. Here again it will be seen from the resulting data reported in 3 Table III that the alloy of the invention attained its ultimate tensile strength and ductility without the solution heat treatment required by the other alloys.

art aluminum-copper and aluminum-magnesium-silicon system alloys.

The alloys of the invention advantageously have a TABLE III Property Condition Al-Mg-Zn Al-Cu Al-Mg-Si Alloy Al y Alloy U.T.S. (K s.i.) {Quenehed at die and 21% drawn 48. 1 39. 6 28. 1 Solution heat treated and 21% drawn 45. 1 49.4 36. 8 Y.S. (K s.i.) "{Quenched at die and 21% drawn 41. 3 34. 1 26. 4 Solution heat treated and 21% drawn 37. 8 42. 9 33. 1 Elong. (percent) [Quenched at die and 21% drawn 14. 3 9. 2 13. 0 [Solution heat treated and 21% drawn 14. 8 9. 2 13.0 R. 01A. (percent) {Quenched at die and 21% drawn 58. O 38. 4 58. 6 Solution heat treated and 21% drawn. 55. 4 36. 3 54.8

The ease of extrudability of the alloy of the invention compares favorably with or exceeds that of the aforementioned prior art alloys as demonstrated by the breaking pressure data reported in Table IV. For each alloy there is given the average value of a number of tests for the breaking pressure required to initiate extrusion. From this data it can be seen that the alloy of the invention had a better extrudability than the prior art aluminumcopper alloy and was comparable with the prior art alu minum-magnesiurn-silicon alloy. Thus, the alloy of the invention can be extruded at least as fast as the aluminummagnesium-silicon system alloy and faster than the aluminum-copper system alloy.

TABLE IV Average breaking pressure,

Alloy: tons/sq. inch Al-Zn-Mg 380 Al-Cu 445 Al-Mg-Si 385 The higher extrusion speed of the alloys of the invention, as well as their ability to develop optimum tensile strength and ductility without solution heat treatment, make possible a significantly lower production cost. Their relatively low critical cooling rate also means that the alloys of the invention can be welded with the same weld metal with the expectation that the weld will age naturally to the parent metal characteristics. In addition, the alloys of the invention exhibit a better machined surface, a more uniform and brighter appearance when anodized, and better corrosion resistance, than the prior zinc content approximately four times that of their magnesium content. Increasing the zinc to magnesium ratio above 4:1 increases the precipitation hardening characteristics of the alloys, and decreasing this ratio increases their solid solution hardening characteristics. Up to about 1'% by weight each of copper and manganese increases the strength of the alloys, and up to about 0.5% by Weight of chromium serves as a grain growth inhibitor or refiner as well as to inhibit stress corrosion. Iron and silicon are generally indigenous impurities and can be tolerated up to a total of about 1% by weight with no significant effect upon the desirable and novel combination of properties of the alloys of the invention.

I claim:

1. An extrudable free machining aluminum base alloy consisting essentially of about 2 to 5.5% zinc, about 0.25 to 2.5% magnesium, about 0.3 to 2.5% bismuth or lead or both, and the balance aluminum.

2. An alloy according to claim 1 in which the ratio of zinc to magnesium contents is about 4: 1.

3. An extrudable free machining aluminum base alloy consisting essentially of about 3.8% zinc, 1.1% magnesium, 0.5% lead, 0.5 bismuth, and the balance aluminum.

References Cited UNITED STATES PATENTS 1,578,979 3/1926 Fuller et al. 75-146 2,215,445 9/1940 Vaders 75-146 2,789,050 4/1957 Ransley 75146 3,287,185 11/1966 Vachet et al. 75146 RICHARD O. DEAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,414,407 December 3, 1968 Albert Jeger It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 29, "the" should read The line 31, after "silicon," insert 0.5% lead,

Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

1. AN EXTRUDABLE FREE MACHINING ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT 2 TO 5.5% ZINC, ABOUT 0.25 TO 2.5% MAGNESIUM, ABOUT 0.3 TO 2.5% BISMUTH OR LEAD OR BOTH, AND THE BALANCE ALUMINUM. 